i am living in UAE. i got E72 with DU network sim card. it was working fine from the day i bought it(march 2010), but since 2 weeks all of a sudden a message showed, SIM REGISTRATION FAILED.
the main problem is that... other DU sim cards and Etisalat network sim cards are working fine on my phone. and my DU SimCard is working fine on other phones.
but somehow my E72 is not working with my DU simcard.
called up customer support of Du, they asked me to get the phone repaired.
the phone shop customer support said that there is a problem with the SIM.

Note: my phone is not locked. bought it from a good phone shop. i do regularly update my phone firmware(means might have the latest firmware installed).
there was no problem till now, just few times the phone got stucked(had to remove the battery and restart it). DU & etisalat are the only 2 network providers here.

It could be you bought a locked phone , which was later unlocked by the retailer/shop ?
After Firmware Update you could have locked it again ?
To find out : it's all about product code , which is printed on the sticker underneath the battery .
Use Google to find Nokia E72 productcodes and check it out .

As the 'author' of the other related post, I think my case is a little different.

As explained, I took the handset into an Orange shop here in the Uk, who checked the IMEI no of the phone and confirmed it had been blacklisted by 'another' network. My sim card works fine with the N95 and my wife's 5800, and other 'foreign' sim cards seem to work with the E72, but not a UK based sim card.

No idea what might be causing this particular posters problem, it *sounds* as though it's the same issue as mine, but if he bought it from a 'reputable' shop, then it must be a different issue?

my phone is not locked.
yestersday i have tried both etisalat and Du sims in my phone and both networks sims are working fine, except my own du sim(this is really wierd).
so the only solution is that to get a new sim.
so probably in few days will get a new sim(with same number)., then lets c what will happen. for the time being using my simcard in old nokia N91.